Alzheimer's disease (AD) is characterized by the accumulation of 13-amyloid peptides (AI3) in the brain. AI3 is generated intracellularly by the regulated cleavage of the 13-amyloid precursor protein (APP). We propose to study the subcellular site(s) where AI3 peptides localize and accumulate with aging, and how this may initiate AD plaque pathology, in transgenic mice carrying familial AD (FAD) mutations. We have recently found that Al342 localizes to multivesicular bodies (MVBs) especially within AD-vulnerable pyramidal neurons in both normal and AD transgenic mouse, and in rat and human brain, but not in APP knockout mouse brain. Since our previous immunohistochemical studies suggested that intraneuronal AI342 accumulation occurs with Alzheimer's disease, we propose to study brain tissue from AD transgenic mice in the process of developing AI3 plaques for evidence of changes in the amount and subcellular distribution of AI340 and AI342 and various APP fragments, also in distal neuronal processes and synapses, using immuno-electron microscopy and subcellular fractionation methods. We plan to assess the amount and subcellular distribution of AI3 peptides at various ages prior and during the time when plaque deposition is known to occur in the specific transgenic AD mice under study; Tg2576 mice expressing the FAD Swedish 670/671 mutant human APP generally develop AI3 plaques at approximately 11 to 13 months of age. In addition, we propose to study the neurobiology and regulation of this MVB-associated pool of AI3 in cultured primary neurons, and to investigate for changes in neuronal MVBs with aging and AD pathogenesis. We hypothesize that accumulation, and potentially aggregation, of AI342 with aging on the outer membrane of MVBs may interfere with the normal transport of vital cargo molecules within neuronal processes. A better understanding of the cellular and molecular events occurring within neurons of the brain involved in AD pathogenesis may be important for the development of more effective molecular based treatment strategies for Alzheimer's disease. [unreadable] [unreadable]